Food safety is a field that has received increased attention in recent years. It has long been known that disease causing microorganisms such as bacteria grow very slowly at low temperatures, multiply rapidly in mid-range temperatures and are killed at high temperatures. For safety, perishable foods must be held at proper cold temperatures to inhibit bacterial growth or cooked to temperatures high enough to kill harmful microorganisms.
Many food handlers, cooks and chefs are of the mistaken belief that color, touch or other visible signs are reliable indicators for determining whether foods are cooked to their“safe state”. As used herein, the term“safe state” refers to a point where the food item has been cooked to an internal temperature high enough and for a sufficient duration to destroy any harmful microorganisms that may be present. The United States Department of Agriculture has determined that color and texture are not reliable indicators of food safety. For example, ground beef may turn brown before it reaches its safe state. A lay food handler preparing hamburger patties and using the brown color as an indicator of doneness is assuming a significant risk that pathogenic microorganisms may survive. On the other hand, hamburger patties cooked to 160° F. and held at least at 160° F. for a minimum of 15 seconds have reached the safe state regardless of their color or texture.
The temperature at which foods reach the safe state varies, as does the safe state temperature for different food items. A roast or steak that is not pierced in any way during processing or preparation and reaches an internal temperature of 145° F. is in its safe state. A lay food handler looking for a visual sign of doneness might continue cooking the steak until it is overcooked and dry. As used herein, “doneness” refers to when a food item is cooked to a desired state and indicates the sensory aspects of foods such as texture, appearance, and juiciness. Unlike the temperatures required to reach the safe state, these sensory aspects are subjective. Likewise, poultry does not enter the safe state until it has reached at least 160° F. throughout. However at this temperature, the meat has not reached a traditional “done” texture and color. Accordingly, many lay food handlers prefer to cook poultry longer (to a higher temperature).
As opposed to relying on visual inspection, food handlers should employ thermometers to ensure that food items have reached their safe state. Thermometers should also be used to ensure that cooked foods are held at safe temperatures until served, i.e., 40° F. or below, or 140° F. and above. However, the present inventors are aware of no thermometer that provides an indication to the user when food items have reached their safe state.
There are a variety of types of food thermometers currently available. Food thermometers are commonly categorized according to the type of temperature sensor they use. For example, there are thermocouple thermometers which measure temperature at the junction of two wires located in the tip of the probe. There are thermistor thermometers which employ thermistors bonded in the tip of the probe typically with epoxy. In addition, there are bimetallic coil thermometers which contain a helix coil in the probe made of two different metals that are bonded together. The metals have different rates of expansion. The coil, which is connected to the temperature indicator, expands when heated.
There are several known thermometers that provide audible alerts when a food item has reached a prescribed temperature. For example, U.S. Pat. No. 3,778,798 discloses a thermistor thermometer that produces an audible alarm when the internal temperature of the food reaches a predetermined level.
U.S. Pat. No. 4,083,250 discloses a portable food thermometer having a probe loaded with a controlled volume of temperature sensitive material. The thermometer includes mechanical components that produce an audible alarm when a preset temperature is reached.
U.S. Pat. No. 6,431,110 discloses a bimetallic thermometer that may be manually preset to a desired temperature. A bimetallic spring is mechanically linked to the alarm mechanism such that the alarm is triggered upon expansion of the spring due to heating.
It is important to note that each of the prior art patents only provide notification when food has reached a predetermined temperature. Such notification may be characterized as a doneness alert. However, food items are not safe to eat until they have 1) reached their safe temperature and 2) remained at their safe temperature for a specified period of time. Thus, none of the foregoing provides the food handler with notification that food items have reached their safe state.
Because of the potentially serious effects of food borne illness, it is particularly important that all food thermometers are accurate. Accuracy of a thermometer is its ability to measure temperature correctly without error. A thermometer must be within ±2° C. (±5° F.) of the actual temperature to be considered an accurate device.
It is recommended that new thermometers be calibrated upon receipt and prior to being put into service. If thermometers are used on a continual basis, they should be calibrated at least once a day. They should also be calibrated whenever they are dropped, and when going from one temperature extreme to another. In addition, in the case of thermistor-based thermometers, they sometimes become uncalibrated because the physical orientation of the thermistor becomes disturbed due to the constant displacement of the probe tip.
The prior art has attempted to address calibration issues by providing calibratable thermometers. For example, U.S. Pat. No. 4,475,823 describes a self-calibrating thermistor type thermometer that employs a calibration circuit including a reference thermistor that produces a corrective signal which is applied to the signal generated by the probe thermistor to compensate for any faulty calibration of the probe thermistor. While this thermistor provides a measure of self-calibration, the accuracy of its calibration is dependent upon the accuracy of the reference thermistor. It is believed that the conditions that cause the probe thermistor to become uncalibrated are likely to cause the reference thermistor to become uncalibrated.
Notwithstanding the usefulness of the above-described products, a need still exists for a calibratable food safety thermometer that notifies the food handler when food items have reached their safe state.